Upgrading Rims and Tires: A Guide
The four little contact patches that grip the road: your tires, are the most significant pieces of real estate on your car. Everything is determined by a few square inches of rubber. Tires are responsible for harnessing the engine’s power, allowing the brakes to do their job, and determining how well a car will go around a turn, whether it’s pulling into a parking slot or roaring into a high-speed sweeper.
Yes, tires bear a significant amount of weight. A complicated combination of cables, rubber, and polymers, all molded into a highly designed contour, makes up that thin round and black doughnut. Then it’s installed on a wheel and inflated with air to give it shape and definition. The designers of your vehicle, tires, and wheels collaborated to create the perfect balance of grip, road feel, ride comfort, noise reduction, and tire wear.
“Bigger is better” has been the dominant trend in America for the past two decades. It used to be that “22s on Porsche trucks” was a flex worth rapping about; now it’s a factory option. Big wheels are no longer simply for performance fanatics who want to equip bigger brakes and tires. They can also just look cool, especially with the taller dimensions of today’s cars. Consider how odd a 2020 Mazda Miata would look with its early 1990s counterpart’s 14-inch factory wheels. It simply wouldn’t work from a design standpoint.
However, there are other practical, everyday reasons to replace your car’s tires and wheels. Some motorists are now opting to defy the trend of larger, heavier wheels with low-profile tires that are more expensive to replace and provide little cushion on bumpy roads. In colder countries, picking up a spare set of wheels and tires to use throughout the summer or winter is also common. If you don’t have to, why damage a finer set of wheels with road salt and grime?
It’s not always true that bigger is better. There’s a size sweet spot that gives you improved grip and those head-turning looks without jeopardizing the original engineering of your vehicle. So, before you upgrade to new rolling stock, let’s go over some fundamentals.
Where it All Began
Despite what Fred Flintstone’s granite-shod convertible would have you believe, the first documented wheels were made of wood. For a long time, automobiles had wooden carriage wheels. Wheels were upgraded to steel, either in a stamped, welded dish or a lighter hub, spoke, and rim form, as increased power and weight rapidly outstripped wood’s limitations. Steel-spoked wheels were popular into the 1950s, notably on small foreign sports cars, but larger American cars required stamped and welded wheels.
Due to the weight penalty imposed by steel, racers and aficionados turned to magnesium, a metal that is as robust as aluminum but even lighter. Unfortunately, unless properly sealed, pure magnesium corrodes quickly and can even catch fire in an accident. Magnesium wheel fires are still mentioned in firefighting training since applying water to a burning magnesium wheel greatly intensifies the fire. Because of the on-road hazards, these earlier magnesium wheels were rarely used outside of racing.
Today’s “mag” wheels are actually a safer, more stable magnesium alloy or, more commonly, an aluminum alloy that has been painted or chromed, as some old-schoolers call them. Beyond these alloys, ultra-lightweight carbon-fiber wheels are now available, but they are still significantly more expensive than an alloy set. For the time being, the majority of wheel modifications are made of aluminum alloys.
The contact patch specifically, how much of the tire meets the ground at any given time—is one of the reasons why people choose larger wheels and tires. Perhaps you’ve upgraded your engine for more power, and now your tires are bursting at the seams just by staring at them funny. To use that more power for something other than crazy burnouts, you’ll need greater contact with the ground.
The contact patch of a tire can be made larger in two ways: by making it longer or by making it wider. The overall diameter of the tire grows as the tread patch lengthens. This works better on a four-wheel-drive vehicle, but most passenger cars will have problems if the tire diameter is increased.
First and foremost, there’s the obvious problem. The tire may rub against other sections of the vehicle, such as the wheel well.
Second, as the overall tire radius increases, the car’s effective gearing increases, robbing it of acceleration. In most cases, gear ratios are expressed as “4.10:1.” The greater the first number, the more the gear multiplies the input torque, which eventually spins your wheels. The problem is that rotating a tire with a greater diameter takes longer.
As a result, if your gearing is set up to rotate the wheels a specific number of times with a smaller-diameter tire, utilizing the same gearing with a larger-diameter tire will not rotate the tire as many times. Because of the greater tire diameter, your 4.10:1 gear ratio may effectively be a “taller” 3.75:1, slowing you down. If you’re serious about changing your car’s gearing to accommodate for this, there are handy calculators online for how a change in tire size impacts your gear ratio.
Furthermore, because your car’s anti-lock braking system isn’t tuned to handle the increased angular momentum caused by all that extra spinning weight concentrated at the rim, it may malfunction. You might not realize it until you slam on the brakes as you approach a slick turn and skid into a hedge.
As a result, we typically go wider with wheels and tires on street cars to enhance the size of that contact patch. While wider tires must fit within your wheel wells without rubbing, it’s typical to increase the width of your wheels by an inch—for example, from a 7-inch-wide rim to an 8-inch-wide rim. This enables for the installation of a wider tire.
You could also want to increase the diameter of your wheels while you’re adding width. Then, for improved handling, you can install a tire with a wider tread and a lower profile. Because of the reduced profile, the overall diameter of your wheel and tire combination remains relatively constant. A Plus 1 upgrade is when the wheel diameter is increased by an inch while the sidewall of the tire is reduced by the same amount. On most vehicles, we can even go further lower in profile with a Plus 2 (for example, going from 16 to 18-inch wheels) or Plus 3 (16 to 19-inch) upgrade without any issues.
Downsizing your wheels works on the same premise as changing the diameter of your wheels by an inch while adjusting for the inch difference in the height of the tire’s sidewall. You won’t notice any changes in your speedometer if you keep the overall diameter of your tires the same. The frequency at which your wheels spin is commonly used by speedometers to calculate your car’s speed. Your speedometer will not give you an accurate speed if you have a considerably different tire diameter that causes your wheels to turn more or less frequently than they used to.
Don’t Over Do It
There are several reasons to be cautious about upgrading your wheels and tires, particularly if your vehicle is less powerful. Tires that are wider have more rolling resistance than those that are narrower, which might reduce your fuel economy. Weightier wheels add bulk, which can have negative repercussions. As previously stated, their increased momentum can interfere with safety features such as ABS, but the added weight also necessitates more power to move, wreaking havoc on both your fuel economy and acceleration. The increased unsprung weight of those wheels can put undue strain on your factory springs and shocks.
A number of things change as the aspect ratio of a tire decreases the that’s reduced profile we’ve been discussing. Because shorter sidewalls are stronger and less supple, the tread moves less. As a result, the steering wheel grip improves, and the road feel improves. That’s fantastic!
A “Plus 1” size upgrade is a 1-in. larger rim diameter and 1-in. wider rim breadth; in this case, the 16-in. rim below. On the 17- and 18-inch wheels, Plus 2 and 3 are featured significantly exaggerated. Choose a tire with a similar height to the factory tire.
The contact patch, on the other hand, becomes more square than oval. On wet roads, the tire’s increased width on the pavement makes it more prone to hydroplaning. Even at low speeds, the rubber has a greater probability of riding on top of the water rather than cutting through it to the concrete. This virtually eliminates grip, which is a Very Bad Thing.
Simultaneously, riding quality declines. The greater danger of wheel damage is one of the key drawbacks of shorter sidewalls. Because of the small sidewalls, the tire rim is more closer to potholes and curbs.
More contact area on the road is provided by a short, wide contact patch, but only if the wheel remains perpendicular (or nearly so) to the ground. The suspension’s task has just become more difficult. A taller, more compliant sidewall deflects more and keeps the contact patch on the ground more easily. The car’s body rolls more with a broader patch and more grip, raising the inner half of the tread off the pavement and diminishing grip. It is possible that handling will suffer if the suspension is not restored.
When searching for new wheels and tires, there’s one more item to consider: how does everything fit together?
Check All the Angles
A centering hub is a raised component of the hub that aligns with a matching recessed element of the wheel in many autos. Its purpose is to keep the wheel centered on the hub more precisely than simply tightening the lug bolts. Some wheels may not fit well in this hub, necessitating the use of a spacer or even a new wheel.
In addition, the replacement wheel must have the proper offset in order to clear the suspension and brakes. The offset is the distance between the hub mounting surface and the centerline of the wheel, which is the point where the rims meet in the middle. It determines how far the tire extends laterally from the wheel hub.
If the rim is wider than stock, the ball joint or steering arm may not have enough clearance to allow half of the extra width to fit inside the wheel well. It might even grind against the fender! Worse, major size changes can throw off steering geometry and cause wheel bearings to overstrain. There are online calculators that show you exactly how a change in wheel and tire size impacts your steering geometry and handling, just like there are for effective gear ratios.
Our recommendation is as follows: Purchase a tried-and-true wheel-and-tire combination developed exclusively for your car or visit a business that specializes in altering your type of vehicle. We can’t blame anyone for wanting something more personalized when wheels come in patterns ranging from cuddly teddy bears to gladiator-like jutting wire hubs.
If you make significant changes to your wheels, you must also make the necessary changes to the rest of your car to ensure that everything functions securely.
How to Choose Rims & Tires